This invention relates to the field of stereotactic surgery, and particularly to curved instruments and method of mapping a curved path for stereotactic surgery for situations where a straight path is impossible or would be more invasive or risky than a curved path.
1. Nomenclature and Definition of Terms
Currently, stereotaxis is generally associated with neurosurgery, and particularly with intracranial surgery. However, in the following description, the terms xe2x80x9cstereotaxisxe2x80x9d or xe2x80x9cstereotactic surgeryxe2x80x9d or xe2x80x9cstereotactic surgical procedurexe2x80x9d shall not be used in that limited sense; rather it should be understood that the term shall be used more generally to distinguish it from the xe2x80x9cconventionalxe2x80x9d surgical procedures where a large incision is made in a patient. Hence, the terms xe2x80x9cstereotaxisxe2x80x9d, xe2x80x9cstereotactic surgeryxe2x80x9d, xe2x80x9cstereotactic surgical procedurexe2x80x9d shall encompass those clinical procedures where a rigid instrument is inserted into a small opening and is navigated, by control of the part that remains outside, to a pre-determined area of a patient""s body. However, frequent references will be made to intracranial surgery as a way of illustrating the invention and its mode of operation, and therefore, such references should not be construed as a limitation on the present invention.
2. Description of the Related Art
Stereotactic surgery (also known as xe2x80x9cstereotaxisxe2x80x9d) is well known to those skilled in the art. It is a special surgical procedure for treating an interior portion of a patient, usually the brain and other intracranial structures, by inserting a rigid probe into a small opening. In conventional open surgery, the surgeon makes an incision large enough for the surgeon to see the path leading to the area of pathology. Stereotaxis, on the other hand, does not require the surgeon to actually see the entire path, so a small opening, only big enough to insert the probe, is required. Hence, stereotactic surgical procedures offer the advantage of minimizing the damage to the tissues surrounding the lesion area, and promotes faster recovery of the patient.
Because a surgeon performing stereotactic surgery does not directly view the inner portions of the brain, he must be able to map out a path and note the sensitivity of the tissues surrounding the damaged area. He must also be able to navigate the probe such that the position of the probe corresponds exactly with the designated path. To achieve the necessary control, a number of apparatus and methods have recently been developed. CAT scan technology, magnetic resonance imaging (MRI), angiography, digital subtraction angiography (DSA) and similar diagnostic procedures are currently used to obtain the visual image of the intracranial area. Such devices are coupled to apparatus, typically a rigid helmet-like framework worn on the skull, or (less invasively but less precisely) markers attached to the skin and xe2x80x98framelessxe2x80x99 guidance system or robot, which precisely positions the probe in accordance with the visual images.
Currently, only straight probes are used in stereotaxis. Hence, only a straight path leading to the selected point can be used. When choosing a straight path, the surgeon selects a path which best avoids sensitive areas or other obstructions. If the path meets a bone, an opening can often be formed by drilling a hole. But if the selected path meets blood vessels, nerves, or brain tissues with important brain functions, a different path must be chosen, or risk causing irreparable damage to the brain.
Not all areas can be reached via a straight path, however. Some sites are so well surrounded by important tissues that no straight path exists where the risk is low. In other situations, a straight path may exist, but the damaged area may be buried deep within the brain requiring a penetration through thick layers of tissues. In still other situations, the path may be confronted by a hard tissue such as calcified dura mater which the probe is unable to penetrate. Lesions in such unreachable places may either be classified as inoperable or be treated using the traditional open procedure.
In some of these situations, a curved path may better avoid the obstructions or sensitive tissues, and reach the intended area with lower risk to the patient. However, at the present, only straight devices are in use, which can follow only a straight path, unless they are allowed to move sideways and create a sheet of damage. To make only a line of damage, the body of the device must slide along the path pierced by the tip. For most curved instruments, however, such sliding movement along a designated curved path is difficult or impossible.
Hence, in light of these shortcomings, it would be desirable to have curved surgical instruments and a method of mapping a corresponding curved path which will not cause significant damage to the surrounding tissue, and which will allow a stereotactic procedure to become a viable option in a greater number of cases.
The method of mapping a curved path for stereotactic surgery involves the selection of a helical-shaped path. The first step is to obtain an accurate image of the pertinent structures of the patient""s internal areas. The image includes the target region and a potential opening site. Using the image, the non-target or high-risk areas surrounding the target region are determined and evaluated for the medical acceptability of passing through them. A curved path which is substantially helical in shape is then selected within the image such that the curve avoids these regions. The corresponding surgical instrument which will be used to follow the selected curved path has a rigid body having a shape which is substantially identical to the path.